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Category:
Natural Sciences

Lecturer:
Paul Nealey, Brady W. Dougan Professor in Molecular Engineering, University of Chicago, USA

Place:
MPI for Medical Research, Seminar Room A/B, Jahnstr. 29

Host:
Prof. Dr. Joachim Spatz, MPI Heidelberg

Description:
Ion transport in block copolymer electrolytesIon conducting polymers play a central role in the development of safer and more efficient electrochemical devices such as batteries, fuel cells, and electrolyzers. Self-assembling polymeric materials with multiple components offer pathways to simultaneously optimize more than one material function, as well as control structure at the nanoscale. In the first part of my talk, I will highlight the advantages and new information that can be derived from the use of custom microfabricated interdigitated electrodes (IDEs) as a platform to probe extrinsic and intrinsic transport properties of polymer electrolytes films through electrochemical impedance spectroscopy (EIS). The second part of my talk will address the use block copolymer electrolytes (BCEs) as ion conducting membranes. BCEs provide the means to realize high ionic conductivity and mechanical robustness by judicious choice of block chemistry. To understand the potential of these materials, however, transport properties through BCEs, with domain structure at the nanoscale, must be understood at a fundamental level at the device scale, 10s to 100s of microns. Extrinsic properties of BCEs depend strongly on the presence of grain boundaries and defects. Conductivity is found to be directly proportional to the number and length of domains of the BCE that are connected from one electrode to the other. Any conducting domain within the film impeded with even a single non-conducting defect (e.g. a dislocation) does not contribute to the conductivity and increases the capacitance of the material. Finally, by completely aligning and connecting the conductive domains between electrodes, we can quantitatively investigate the intrinsic transport properties of BCEs and compare them to their homopolymer analogs. We conclude that the interfacial mixing between the blocks at domain interfaces is the dominant factor in reducing ionic mobility in BCEs, reducing the expected conductivity based on volume fraction by as much a factor of 2.

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